The present invention relates to fluid pressure operated disc brakes and particularly to disc brakes for an air brake equipped vehicle such as relatively large sized trucks and buses, for example.
Disc brakes are commonly used in today's passenger cars and lighter commercial type vehicles, which have hydraulic or hydraulic/pneumatic brakes. Consequently, any increase in the brake cylinder volume due to increased piston stroke resulting from brake shoe wear is compensated without requiring a mechanical slack adjuster by drawing additional hydraulic fluid from a relatively small storage reservoir, which is a part of the closed hydraulic system. A brake system of this type is ideal in that no additional expense or space is required to accommodate a slack adjuster.
In contemplating the application of disc brakes to larger type commercial vehicles, however, consideration must be given to the fact that these vehicles typically employ air brakes. This creates the problem of compensating brake shoe wear, which requires either a larger air tank to accommodate the additional brake cylinder volume and/or more efficient compressor. Neither of these choices is practical because of limited space for a larger air tank and the additional expense of a compressor having the necessary capacity to handle the air requirement. An alternative choice, of course, would be to resort to a mechanical type slack adjuster to maintain the piston stroke and thus the effective brake cylinder volume constant as brake shoe wear progresses.